PMMA Flashcards
by what reaction is PMMA produced
free radical addition polymerisation
what type of monomers join together to make PMMA
methacrylate monomers
what are the 4 stages in acrylic resin polymerisation
1 - activation of initiator to produce free radicals
2 - initiation - free radicals break c=c bonds
3 - propagation - growing polymer chain
4 - termination
what are the 2 methods of activation and what is most commonly used
heat cured - most common
self cure
what is contained within the powder and liquid of heat cured acrylic
powder - initiator (benzoyl peroxide) , PMMA particles (speeds reaction) , plasticiser, pigments, co polymers (mechanical properties)
liquid - methacrylate monomer, inhibitor (prolongs shelf life) , co polymers (mechanical properties)
what effect can curing at to high a temperature lead to
a high temp is needed to give good mechanical properties however too high and it can cause voids due to gaseous porosity
what can happen if cooled to quickly
mould and acrylic have different expansion coefficients , cooling too quick can cause internal stresses which decrease mechanical properties e.g compressive strength
contraction porosity vs gaseous porosity
gaseous - occurs in bulky parts where monomer exceeds 100 degrees , curing should be a slow process at polymerisation = exothermic
contraction - can occur in areas where dough is not sufficiently packed
porosity affects strength , appearance and may absorb saliva
what is acrylics thermal conductivity and softening temp like
it is low which isnt good - risk of scalding
softening temp = around 75 so fine for hot foods but cant be cleaned in boiling water
is PMMA toxic or irritant
no , only irritant if monomer under cured
what is PMMAs mechanical properties like
they are poor , material is increased in bulk to compensate but this offsets its advantage of having a low density
